1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a secondary battery that sheathes a protection circuit board with a separate cover in advance and connects the sheathed protection circuit board to a bare cell and then executes a molding or hard pack operation with a molding resin member in a space between the protection circuit board and the bare cell.
2. Description of the Related Art
Generally, a secondary battery, which is contrary to a primary battery, denotes the battery capable of recharging and discharging and the secondary battery is widely used in compact hi-tech electronic apparatuses such as cellular phones, PDAs and notebook computers. Particularly, a lithium secondary battery has an operating voltage of 3.6V which is three times as much as that of a conventional nickel-cadmium battery or nickel-metal hydride battery, and a relatively higher energy density per unit weight, thus the market demand for the lithium secondary battery dramatically increases.
According to the lithium secondary battery, a lithium based oxide is used as a positive electrode active material and a carbon material is used as a negative electrode active material. Also, the lithium secondary battery is manufactured in various shapes, for example cylinder, rectangular and pouch shape.
Further, a rectangular secondary battery is composed of a rechargeable bare cell formed in a rectangular shape and a protection circuit module when the constitution of the secondary battery is explained on the basis of the rectangular shape.
The bare cell may be constructed with an electrode assembly, a can in an approximate rectangular shape receiving the electrode assembly, and a cap assembly sealing the can by being connected to an opening of the can.
The protection circuit module is a safety device which prevents the battery from ignition and explosion by blocking a current when the internal temperature or the voltage of the battery increased. The protection circuit module is composed of a protection circuit board on which various electrical elements are mounted, and the protection circuit board is connected to the bare cell via a conductor so called a lead plate.
The form, in which the protection circuit board is connected to the bare cell, is referred to as a core pack. The secondary battery may be used in the form of the core pack, however, the secondary battery is generally used in the form that utilizes molding or a separate exterior case as a structure covering a space between the bare cell and the protection circuit board and the surface of the protection circuit board. Here, the battery type, in which the core pack is covered by the separate exterior case, is generally referred as a hard pack or hard pack battery, thus the terms (i.e. hard pack and hard pack battery) are used when necessary.
According to the secondary battery manufactured by molding the space between the bare cell and the protection circuit module with a molding resin member, however, the molding is executed even on the surface on which an external terminal is installed, and thus several problems are generated.
For example, the amount of the molding resin member is relatively high because the space between the bare cell and the protection circuit board to be molded is relatively broad. The space between the bare cell and the protection circuit board is bent several times and is extended to one surface of the external terminal, thus the operation of inserting the molding resin member into the space needs to be precisely executed. Such contemporary insertion of the molding resin member may deteriorate the productivity of the secondary batteries. Furthermore, there is a possibility that the molding resin member is improperly supplied to the space between the protection circuit board and the external terminal which extends and meanders. The difficulty of accurate application of the molding resin may cause a problem that one surface of the external terminal of the protection circuit board may be improperly covered, therefore, the external terminal may fail to be protected from external impacts. It is almost impossible to have one surface of the external terminal of the protection circuit board to be thickly molded by the molding resin member considering the entire thickness of the secondary battery, therefore the structural stability of the secondary battery is reduced because one surface of the external terminal of the protection circuit board is protected by a thin, low-strength resin layer.
In accordance with the secondary battery manufactured by covering the bare cell and the protection circuit module with a separate exterior case, the exterior case has to be formed to cover the outer part of the protection circuit board, and thus the amount of the material required for the exterior case is increased and the mold structure for the exterior case is getting complicated. Therefore, manufacturing costs may increase. Furthermore, the exterior case has to have a sufficient thickness, since the conventional exterior case accommodates the entire core pack or covers multiple surfaces of the core pack and the conventional exterior case is manufactured by a technique of injection molding. Therefore, it is almost impossible to mold moldings with a thin thickness, and the conventional exterior case can hardly have a sufficient thin thickness. This is also applied to a cover surface of the protection circuit board and serves as a reason to increase the over-all length of the secondary battery.
There is another problem that the manufacturing process of the secondary battery is complicated, because it is essential to check whether or not the external terminal is exposed to the outside of the exterior case while being packed.